Four Winding Transformer modelling

[simatic7]

Hi
I am looking for a help in four winding transformer . Does anybody have equivalent circuit of a four winding transformer. Recently I came across a four winding transformer with the following specification.
22kV/690V/690V/415V
1MVA/1MVA/500kVA
4.48%/5.13%/7.18%.
I confirmed from the client and they said its four winding transformer but by looking at the rating and percentage imp , it seems to me it is three winding transformer but looking at voltage again it seems it is four winding transformer.
Can anybody highlight something about four winding transformers and how to model it . For example three winding transformer can be modelled with two - 2 winding transformer ?
I have also attached the nameplate details (? ) of transformer taken from single line diagarm.

http://files.engineering.com/getfil...4e8db7ed0ff&file=four_winding_transformer.bmp

Your help is kindly appreciated.
Regards
SImatic

 

[juleselec]

What kind of analysis do you want to perform?
If you just want to run some load flows and balanced short circuits, then you could get away with modelling it as three two-winding transformers.

It gets trickier if you want to calculate unbalanced faults. You'll definitely need more information to model the zero-sequence impedances (e.g. measured impedances with various combinations of open- and short-circuited windings).

For EMT studies, you'll need more information still.

 

[prc]

I am not sure while modelling three winding tarnsformers, considering it as two numbers two winding transformers is the correct approach.Normally it is converted in to a Y circuit with individual impedances calculated for each circuit. For 4 winding transformers it is bit more complicated. You can get more details from the chapter (theory of multi circuit transformers) in Transformer Engineering by LF Blume & A Boyajian(1951).There are couple of IEEE papers also available on the subject.Some numerical calculations can be seen in the volume"Transformer Reference book" bY Allis chalmers(1954)

If you can give impedances for all combinations of windings with their MVA base, I can try and give the mesh circuit.

 

[simatic7]

Till now i want to do just load flow, balance and unbalanced short circuit. Recently I came to know we can also model zero seq impendance my modifying similar three winding transformer zero seq circuit with additional winding. But still not 100% clear about this . If anybody has further elaborated doc , please let me know.
regards
Simatic